Regulated power supplies or voltage regulators are typically required to provide the voltage and current supply to microelectronic devices. The regulator is designed to deliver power from a primary source to an electrical load at the specified current, voltage, and power efficiency. Switching power converters (SPC), also referred to as buck regulators, are commonly used voltage regulators due to their high efficiency, high current capability, and topology flexibility. In addition, they can be designed to provide very precise voltage and current characteristics required by devices such as microprocessors, microcontrollers, memory devices, and the like.
Power requirements for emerging leading edge technology microprocessors have become very difficult to satisfy. As the speed and integration of microprocessors increases, the demands on the power regulation system increase. In particular, as gate counts increase, the power regulation current demand increases, the operating voltage decreases and transient events (e.g. relatively large voltage spikes or droops at the load) typically increase in both magnitude and frequency. Some emerging microprocessors are expected to run on less than 1.3 volts and more than 100 amperes.
SPCs utilizing step-down multi-phase buck converters have been the preferred topology to meet the low voltage and high current requirements of microprocessors. With the advent of increasingly complex power regulation topologies, digital techniques for power converter control, specifically in multiphase designs, can improve precision and reduce the system's total parts count while also supporting multiple applications in the same power system through digitally programmable feedback control.
Existing feedback controls take voltage and current measurements from the load, as well as from the individual output phases. The feedback information has been used to adjust the duty cycle, i.e., width of the pulses produced by each of the phases of a multi-phase buck regulator system, to bring the supplied voltage and current within the load line tolerances specified by the microprocessor manufacturer. Such multi-phase pulse width modulated (PWM) voltage regulator systems have been used in a variety of environments and applications.
Active Transient Response (ATR) has been used for high frequency response to rapidly changing power requirements at the load by quickly activating multiple phases to source or sink (as the case required) more current to or from the load, thereby temporarily overriding the generally slower overall voltage regulator system response. ATR enables voltage regulator systems to be designed with lower overall output capacitance while maintaining equivalent dynamic performance. An ATR circuit includes a window comparator that compares the output supply voltage at the load to the reference voltage, as determined by the specified load line. As long as the output voltage remains within a specified tolerance range (i.e., window) above or below the specified load line, the ATR circuit provides no input signal to the PWM, which proceeds to provide power to the load in a conventional manner. On the other hand, as soon as the voltage is outside the “window”, the ATR circuit signals the PWM to modify its operation. For example, if the voltage drops below the specified voltage range, all low-side power switches in the multi-phase system are turned off and then, after a short delay, all high-side power switches are turned on, causing the normally staggered inductor charging to occur in parallel.